Primarily, hydrogen is produced industrially by catalytic steam reforming of nonrenewable methane at temperatures of 400-1000° C. and at steam partial pressures near 30 bar. Hydrogen production from renewable biomass is particularly challenging due to sluggish catalytic rates in water (the most common biomass contaminant) and catalyst deactivation. Furthermore, H2 transportation and storage present safety issues. However, such concerns could be addressed using a carrier which released H2 on demand, such as biomass-derived methanol, ethanol, or formic acid, all of which are compatible with direct alcohol fuel cell technologies. The state-of-the-art for sustainable, environmentally benign methanol and ethanol production typically employs biomass (e.g., cellulose) fermentation to “bioalcohols” containing ˜10% alcohol in aqueous solution. Note that this bioalcohol is produced with negligible net carbon emission.
Regarding H2 production from alcohols, the prior art literature describes several catalytic systems. A heterogeneous Pt/Al2O3 methanol reforming catalyst was reported to operate at 200-225° C. and pressures of 25-50 bar in aqueous media. In another study, using a homogeneous Ru pincer catalyst, 3 equiv. of H2 can be produced from MeOH+H2O under moderate temperatures (72-95° C.), inert atmosphere, and ambient pressure. Note, however, that this conversion required strong base and is driven thermodynamically by stoichiometric CO2/carbonate formation. The Ru pincer also operates in 9:1 H2O:MeOH solution, albeit with a 18× reduction in TOF (265 h−1) versus that in neat MeOH, (4719 h−1). Other examples of homogeneous alcohol dehydrogenation by homogeneous Ru, Ir, and Fe catalysts bearing non-innocent ligands were reported. Many of these systems require stoichiometric strong base such as KOH for turnover and yield carbonates or CO2 as co-products. While these homogeneous catalytic studies demonstrate that methanol and ethanol reforming are possible at low temperatures and pressures, they often require expensive metals and ligands requiring complex air-free synthesis and handling.
Roughly 30% of all methanol production worldwide is used to produce formaldehyde (˜30 million tonnes annually), the starting material for a myriad of plastics and resins. Most formaldehyde is produced oxidatively using methanol, steam, and air at temperatures as high as 800° C. and at pressures near atmospheric. An efficient catalytic system that produced aldehydes and clean H2 fuel from bioalcohols at moderate temperatures and pressures, without greenhouse gas co-products, would clearly be of great interest and represent an advancement in the art.